/Engine/Source/Runtime/Foliage/Public/InstancedFoliageActor.h
Default InternalTakeRadialDamage behavior finds and scales damage for the closest component which isn't appropriate for foliage.
virtual float InternalTakeRadialDamage ( float Damage, struct [FRadialDamageEvent](API\Runtime\Engine\Engine\FRadialDamageEvent) const & RadialDamageEvent, class [AController](API\Runtime\Engine\GameFramework\AController) * EventInstigator, [AActor](API\Runtime\Engine\GameFramework\AActor) * DamageCauser )